In closed water areas such as lakes, ponds, dams and reservoirs, where any water flow is scarce and is retained for a long time, water-bloom, algae and the like floating on water, if left untreated in a natural state, thrive with high density and decay, which eventually pollutes the water. A conventional method employed for removing water-bloom and algae is, for example, to catch and collect it with a net or the like from a boat. Such an operation, where water-bloom and algae are collected manually, has limited efficiency and takes considerable time when operating on large lakes.
Recently, another kind of purifying device has come into use, which destroys cells of phytoplankton such as water-bloom by a single use of ozone, ultrasonic waves, ultraviolet rays or the like, bringing a marked improvement in efficiency of purification operations in closed water areas. However, most of the conventional purifying devices treat water by blowing ozone into water or collecting sludge-formed decayed substances accumulated on the water bottom.
Therefore, water-bloom and algae that are floating on water in particular cannot yet be collected without operations using boats, hindering complete purification in closed water areas. In view of this, the present inventor proposed, in Japanese Patent Application No. 2000-289005, a purifying device for rivers and lakes which has an improved degree of purification by efficiently decomposing water-bloom and algae and releasing oxygen only.
In the above purifying device for rivers and lakes, water adjacent to the water level is sucked in with a submersible pump, then oxidizing gases such as ozone are added and dissolved in the water sucked in by the submersible pump, and the resulting water is discharged to the rivers or lakes, thereby removing water-bloom and algae near the water level as well as rapidly decomposing them when ozone is used.
With this purifying device, as algae such as water-bloom is collected together with water by suction power of the submersible pump, the submersible pump should have larger suction power in order to increase the speed of sucking in algae to purify water. However, larger suction power would increase the electric power consumed by the submersible pump.
In view of the above problem, an object of the present invention is to provide a purifying device requiring less electric power and that is capable of rapidly collecting floating substances such as water-bloom and algae to purify water in closed water areas with higher efficiency.